Audio drivers rework:
- nuked QMidiEventQueue, incoming events are now supposed to be timestamped on the fly and added to the internal synth's queue
- common timing-related methods and fields moved to abstract AudioStream class
- audio drivers adopted to the new design
- removed from WinMM driver those paranoid x-run checks (moreover, incorrect for Vista+)
- more code cleanup
QtAudioDriver improvement:
- rendering is performed in a dedicated thread instead of the main thread to improve audio smoothness
- fixed timing problem with clocksync at startup
- Added timeout when closing WinMMAudioDriver driver